1. Field of the Invention
This invention relates generally to a device for distributing a developer over the surface of the photosensitive film of a film unit in a self-development type photographic camera, and more particularly to a pressure applying device for giving force to a pair of pressure applying rollers which are adapted to apply compressive pressure to the film unit as it is advanced therebetween for distributing the developer liquid over the surface of the exposed photosensitive film.
2. Description of the Prior Art
In the conventional self-development type photographic cameras, a film unit comprising a photosensitive film, a transfer sheet superposed thereon and a rupturable pod attached to one end of the film is advanced between a pair of pressure applying rollers so that the pod is ruptured by the compressive pressure applied thereto and the developer liquid contained therein is uniformly distributed over the surface of the photosensitive film. The uniform distribution of the developer liquid, initiates the diffusion transfer process and a photographic image is obtained on the transfer sheet. Therefore, the quality of the image obtained on the transfer sheet depends upon the uniformity of distribution of the developer liquid between the photosensitive film and the transfer sheet. In order to improve the uniformity of distribution of the developer liquid on the film, various devices have been proposed in conventional cameras for uniformly applying pressure to the pair of pressure rollers.
One of the conventional means for giving pressure to the pair of rollers comprises a pair of U-shaped springs provided at the opposite ends of the rollers for giving compressive force to the pair of rollers. This type of pressure applying means is advantageous in that the rollers can be removed from the camera and can accordingly be conveniently washed.
Another example of a conventional means for giving pressure to the pair of rollers comprises a twisted spring made of piano wire or the like extending in the direction of the pressure applying rollers and working at both ends thereof to press the shaft of one roller toward the other. This type of pressure applying means is also advantageous in that the rollers can be easily removed from the camera.
Since little space exists in the camera in the direction of the pressure application to the rollers, i.e. the direction normal to the plane in which the film unit advances, the pressure applying spring or springs of conventional pressure application means have a complicated shape and accordingly are difficult to manufacture. When such springs are mass-produced, there result small variations in the characteristics and shape of the springs which cause slight but critical differences in the pressure of the springs when used in the pressure application means. Further, the conventional springs of this type are disadvantageous in that it is very difficult to finely control the pressure thereof once they are mounted to the camera.